The general field of the invention is the detection of the presence of detection indicia on moving members and more particularly this invention is concerned with the detection of indicia which have been deliberately applied to a controlled document which is moving at high speed relative to a detecting apparatus or stations.
Controlled documents as referred to herein comprise stock or other types of certificates, tickets, coupons, bonds and notes, evidence of state obligations and the like which are imprinted with subject matter and patterns that may include dates, values, and other critical information. In the handling of such controlled documents as for example where involved in exchange, redemption, business transactions and the like it is basic that the document be identified as genuine and that its date and/or value be ascertained. Manual handling of such controlled documents depends upon the skill and speed of the handlers to make the necessary identification. In the case of controlled documents which are required to be handled in large volume, even where it may be presumed that all are genuine, such simple matters as counting the documents and coincidentally recognizing and recording their values become difficult. When the genuineness of the documents must be determined simultaneously the difficulty is exacerbated.
The solution to the problem of high speed determination of the character of the controlled documents has been approached by others through the provision of an apparatus which automatically attempts to pass the documents through said apparatus and sense the character of the documents. Some of these approaches are represented by U.S. Pat. Nos. 3,132,242; 3,000,498; and by various apparatuses which are used for detecting and sorting cards and recording information carried thereon. Patents concerned with the latter type of apparatus comprise U.S. Pat. Nos. 2,294,751; 3,519,802 and 2,294,681.
Other prior art which is generally concerned with this field relates to the detection of substances on paper as in U.S. Pat. No. 3,043,993; detecting nonuniformity in electrical cables as in U.S. Pat. No. 3,096,478; and detecting and using information carried on tapes as in U.S. Pat. Nos. 3,440,642; 3,467,957 and 3,422,400.
The functions which can be performed by the apparatus contemplated in accordance with the invention are generally capable of being performed by the prior art devices mentioned above, albeit not with the same reliability and speed. These functions include sorting, ejecting spurious documents, recording information, counting and indicating certain conditions by visual displays and/or oral alarms.
Some of the problems which beset the prior art structures are concerned with the detection of the character of worn and soiled controlled documents and the interference produced by the leading and trailing edges of documents which are being passed individually through the apparatus.
Detection of information carried on cards which are all identical in texture and in which the information is applied by punches or magnetic spots is not as difficult as the detection of information carried on a controlled document which is or may have been in circulation and where the identifying information has been applied in a manner which produces no visibly or mechanically detectable changes in the document.
In the case of the invention, the information is applied by detection indicia which may either be fully integrated with the pattern carried upon the controlled document or which may be applied in a manner which renders the same invisible, not only to human sight but likewise invisible to the type of light beams used for photodetection.
The apparatus which is required to detect the character of controlled documents comprises an expense in any establishment which must be compared with the returns resulting from its use. If the reliability and the speed of the apparatus are insufficient to eliminate the need for human monitoring then the expense of the apparatus will not be justified. The invention is believed to be moe reliable and to operate with greater speed than known apparatus which attempts to do some or all of the functions of the apparatus of the invention.
The apparatus of the invention is adapted for use in the case of either individual controlled documents being passed through the same or in the case of continuous ribbons or webs of substrate material. Successive operations on the controlled document or web can comprise punching, printing, registering, folding, cutting and so forth. These could be in addition to the functions of recording, counting, ejecting, etc.
The detection indicia which is applied to the controlled document, as indicated above, can be integrated with the normal printed pattern, imprinted upon the document or can be invisible in the form of a strip, band or area of some substance which cannot be seen by the human eye. Further, the detection indicia can be of a nature which permeates through the substrate so that it is detectable from either face. As will be explained, one of the requirements of the material from which the detection indicia is formed is that it have a resistivity which differs substantially from the resitivity of the substrate to which or upon which it is applied. In the case of any detection indicia which is permeated through the substrate the apparatus will necessarily have a dielectric layer which separates it from the base or mandrel upon which the document moves to aid in establishing the capacitive elements which will be described.
The invention is believed to be unique in that an apparatus according to the invention is capable of detecting invisible detection indicia carried on worn and even tattered documents where said detection indicia has been practically exhausted or worn off. Further, the invention is important over the prior art from the standpoint that the type of detection which has been mentioned above of worn and used controlled documents can be carried out at linear speeds of the order of 10 to 15 meters per second. Such speeds are attainable even though the detection indicia is invisible.
Another aspect of the invention is that the method and structure of the invention produce a type of signal which is relatively greater than the signals of the prior art devices, with a better signal to noise ratio; hence easier to detect and more reliable.